When I was a young man I had much ego (自负). I thought I 1 everything. I looked forward to fame and success. I can even remember once in college2 telling one of my friends: “If only everyone listened to me, then they would all be happy.” I 3 left school, ready to take on the world. Little did I know the world was about to take on me.

    In the 4following college, instead of success, I found struggles. I had 5 in finding work. My jobs were either temporary or were 6 badly. When my wife and I had children, we were 7 to learn that both of our sons had Autism (自闭症) and would need to be 8 for the rest of their lives. I had no 9why this had happened to us.

    In time, however, I began to 10. My ego was decreasing fast. Instead of success, I found my 11 in moments of love. Playing and 12 with my sons brought me so much happiness. My boys 13me more about peace, patience, joy and love than I could have ever learned on my own. I began to share the 14I learned through my writings and my life. I finally realized that my 15 in this world had nothing to do with fame or success.16 it had everything to do with allowing love and light into my life and 17 it with everyone I could.

    You may not be happy 100% of the time18 can be in this world. Yet, you will find a joy no earthly (世俗的)19 could ever give. Put all of your moments, days, and years to good use then20 them with love.

已知四边形ABCD是边长为4的正方形，以AB为直径在正方形内作半圆，P是半圆上的动点（不与点A、B重合），连接PA、PB、PC、PD．
(1)如图①，当PA的长度等于    时，∠PAB＝60°；当PA的长度等于     时，△PAD是等腰三角形；
(2)如图②，以AB边所在直线为x轴、AD边所在直线为y轴，建立如图所示的直角坐标系（点A即为原点O），把△PAD、△PAB、△PBC的面积分别记为S₁、S₂、S₃．坐标为（a，b），试求2 S₁ S₃－S₂²的最大值，并求出此时a，b的值．